The present invention relates to a beam position detector for receiving a laser beam from a rotary laser irradiating apparatus, which projects the laser beam by rotary irradiation, and for displaying a photodetecting position.
In the field of civil engineering and architectural engineering, a laser survey system is used to form a reference plane. The laser survey system comprises a rotary laser irradiating apparatus and a beam position detector, and a laser beam is projected for rotary scanning from the rotary laser irradiating apparatus. By the laser beam, a reference plane is formed, and a scanning position of the laser beam is detected by the beam position detector.
Now, description will be given on a laser survey system referring to FIG. 6.
In this figure, reference numeral 1 represents a rotary laser irradiating apparatus, and 2 represents a beam position detector.
The rotary laser irradiating apparatus 1 is installed on a tripod (not shown). The rotary laser irradiating apparatus 1 has a rotator 3 on its upper portion. From the rotator 3, a laser beam 4 is projected in horizontal direction and is rotated for total circumferential scanning. On the rotary laser irradiating apparatus 1, an operation panel 9 for defining leveling operation, scanning speed of the laser beam and range of scanning, etc. and for operating the rotary laser irradiating apparatus 1 is provided.
The beam position detector 2 comprises a photodetection unit 5 for detecting the laser beam and a display unit 6 for displaying a photodetecting position. On each of the lateral ends of the beam position detector 2, a notch 7 is formed.
At an irradiating position of the laser beam 4 on wall surface, for example, the beam position detector 2 is supported. The photodetection unit 5 detects a passing position when the laser beam passes through. The display unit 6 notifies that the irradiating position of the laser beam 4 with respect to the beam position detector 2 is adequate based on the results of detection by the photodetection unit 5. If the position is deviated, it notifies a direction of deviation or a direction to be corrected by a display pattern 8. In case the position of the beam position detector 2 is adequate and not deviated, a mark is put using the notch 7. The mark thus formed serves as an index for a reference position.
Next, description will be given on the beam position detector 2.
As shown in FIG. 7 (A) and FIG. 7 (B), the photodetection unit 5 of the beam position detector 2 is divided to a first photoelectric conversion unit 10 and a second photoelectric conversion unit 11. The first photoelectric conversion unit 10 and the second photoelectric conversion unit 11 are both designed in triangular shape and are at positions of point symmetry to each other.
Referring to FIG. 7 (A) and FIG. 7 (B), description will be given now on photodetecting status on the photodetection unit 5 and further on scanning position detecting status of the laser beam.
When the laser beam 4 scans over the photodetection unit 5, lengths L1 and L2 of line segments, along which the laser beam 4 goes across the first photoelectric conversion unit 10 and the second photoelectric conversion unit 11, vary according to vertical position of the photodetection unit 5. If the laser beam 4 goes across the graphical center of the photodetection unit 5, the line segments are given as: L1=L2. If the scanning position of the laser beam 4 is deviated from the graphical center of the photodetection unit 5, e.g. in case it is lower than the graphical center, the following relationship exists: L1 less than L2.
Photodetection amount (or received light quantity) of each of the first photoelectric conversion unit 10 and the second photoelectric conversion unit 11 is proportional to the length of the line segment, along which the laser beam 4 is projected, and output value of each of the first photoelectric conversion unit 10 and the second photoelectric conversion unit 11 is proportional to the photodetection amount respectively. By comparing signal level of relative ratio of the output value from each of the first photoelectric conversion unit 10 and the second photoelectric conversion unit 11, it is possible to determine the scanning position of the laser beam 4 with respect to the photodetection unit 5. As described above, in case the scanning position of the laser beam 4 is deviated from and lower than the graphical center of the photodetection unit 5, and if the first maximum photodetection amount is compared with the first maximum photodetection amount, output value from the first photoelectric conversion unit 10 is lower, and output value from the second photoelectric conversion unit 11 is higher.
By comparing the output value of the first photoelectric conversion unit 10 with that of the second photoelectric conversion unit 11, it is possible to determine the scanning position of the laser beam 4. Also, according to the display on the display unit 6 as described above, a position to set the beam position detector 2 is also found.
As described above, in the beam position detector 2, the difference of the photodetection amount between the first photoelectric conversion unit 10 and the second photoelectric conversion unit 11 (i.e. the difference between the first maximum photodetection value and the second maximum photodetection value) is compared, and the scanning position of the laser beam with respect to the photodetection unit 5 is detected. In this way, by detecting relative value of the output of the photoelectric conversion units, it is possible to accurately detect the scanning position even when intensity of the laser beam itself is low and regardless of the size of diameter of the laser beam.
However, as shown in FIG. 8 (A), the photodetection unit 5 is usually placed at retreated position with respect to a photodetection window 12 of the beam position detector 2. There is no problem in case the laser beam 4 is projected perpendicularly to the photodetection unit 5, but if the laser beam 4 enters obliquely as shown in FIG. 8 (A) or FIG. 8 (B), a shadow 13 is formed by the beam position detector 2 itself. In case the laser beam 4 is scanned with the shadow 13 formed in this way, the second photoelectric conversion unit 11 does not detect the laser beam 4 in the shadow 13. As a result, the length of line segment of the laser beam 4 detected by the second photoelectric conversion unit 11 is turned to L2xe2x80x2, exempting the portion of the shadow 13, and this is shorter than the length of the line segment L2, along which the beam actually is projected. Therefore, this means that relative value of the photodetection amount extensively varies between the first photoelectric conversion unit 10 and the second photoelectric conversion unit 11. This leads to the decrease of the accuracy to detect the scanning position of the laser beam 4 by the beam position detector 2.
It is an object of the present invention to provide a beam position detector, by which it is possible to perform accurate position detection without being influenced by the shadow even when a laser beam is not projected perpendicularly toward the photodetection unit.
To attain the above object, the beam position detector, according to the present invention comprises a photodetection unit for receiving a laser beam and issuing a signal corresponding to photodetection amount, wherein said photodetection unit is divided to divided portions symmetrical to each other by a division line running perpendicularly with respect to position detecting direction, said divided portions are further subdivided to a plurality of subdivided sectors, some of the subdivided sectors of one of the divided portions and some of the subdivided sectors of the other of the divided portions constitute a first photoelectric conversion unit, the rest of the subdivided sectors of one of the divided portions and the rest of the subdivided sectors of the other of the divided portions constitute a second photoelectric conversion unit, and width of said first photoelectric conversion unit is gradually decreased in positive position detecting direction, and width of said second photoelectric conversion unit is gradually increased in positive position detecting direction. Also, the present invention provides the beam position detector comprises a photodetection unit for receiving a laser beam and issuing a signal corresponding to photodetection amount, wherein the photodetection unit is divided to divided portions symmetrical to each other by a division line running perpendicularly with respect to position detecting direction, the divided portions are further subdivided to a plurality of subdivided sectors, at least one of the subdivided sectors of one of the divided portions has a geometrical form having a part of the division line as a base thereof and having a portion with width thereof gradually decreased in positive position detecting direction, and at least one of the subdivided sectors of the other of the divided portions has the base in common and has a geometrical form having width thereof gradually decreased in negative position detecting direction, wherein the geometrical form having width thereof gradually decreased in positive position detecting direction of one of the divided portions and the geometrical forms except the forms having width thereof gradually decreased in negative position detecting direction of the other of the divided portions constitute a first photoelectric conversion unit, the geometrical form with width thereof gradually decreased in negative position detecting direction of the other of the divided portions and geometrical forms except the forms having width thereof gradually decreased in positive position detecting direction of one of the divided portions constitute a second photoelectric conversion unit, and width of the first photoelectric conversion unit is gradually decreased in positive position detecting direction, and width of the second photoelectric conversion unit is gradually increased in positive position detecting direction. Further, the present invention provides the beam position detector as described above, wherein the division line is further divided so that the base is equal to the remaining part of the division line except the base. Also, the present invention provides the beam position detector as described above, wherein divided forms of two divided portions are symmetrical to each other with respect to the division line. The present invention further provides the beam position detector as described above, wherein the photodetection unit has a symmetrical line running perpendicularly to the division line and the divided forms are symmetrical to each other with respect to a symmetrical line. The invention further provides the beam position detector as described above, wherein variation amount of width of the first photoelectric conversion unit and variation amount of width of the second photoelectric conversion unit have a higher change ratio near the division line. The present invention also provides the beam position detector, wherein the geometrical form having a part of the division line as a base thereof and having a portion gradually decreased in position detecting direction has two divided line segments in the central portion of the division line divided into four line segments with equal length as a base thereof. The present invention also provides the beam position detector as described above, wherein the division line is divided into four divided segments with equal length, and the two divided portions have respectively a geometrical form having two central divided line segments each as a base thereof and with width thereof gradually decreased in position detecting direction and two geometrical forms having a divided line segment on each side as a base thereof and with width thereof gradually decreased in position detecting direction, wherein the first photoelectric conversion unit comprises two geometrical forms each on one side and having width thereof gradually decreased in positive position detecting direction of one of the divided portions and the remaining part of the portion except the two geometrical forms and having width thereof gradually decreased in negative position detecting direction of the other of the divided portions, and the second photoelectric conversion unit comprises the remaining part of the portion except two geometrical forms each on one side and having width thereof gradually decreased in positive position detecting direction of one of the divided portions and two geometrical forms one on each side and having width thereof gradually decreased in negative position detecting direction of the other of the divided portions. The present invention further provides the beam position detector as described above, wherein two or more geometrical forms each having a part of the division line as a base thereof and having a portion with width thereof gradually decreased in position detecting direction are formed on each of the divided portions, the division line is equally divided to sectors in multiple number of 4, and the geometrical form having a portion with width thereof gradually decreased in the position detecting direction has two divided line segments for every two other divided line segment except the one divided line segment on each end of the division line as a base thereof. Further, the present invention provides the beam position detector as described above, wherein there are further provided a signal processing unit for detecting a light beam incident position based on a signal from the photodetection unit and a display unit for displaying information relating to the projecting position of the laser beam based on a signal from the signal processing unit. Scanning position of the laser beam is detected by comparing the output value of the first photoelectric conversion unit with the output value of the second photoelectric conversion unit. Even when a shadow is formed on the photodetection unit, it is formed evenly over the first photoelectric conversion unit and the second photoelectric conversion unit, and it does not adversely affect the detection of the center position.